Extinguishing agents for magnesium fires



March 18, 1958 s. l. RICHMAN ETAL 2,827,431

EXTINGUISHING AGENTs'FoR MAGNESIUM FIRES Filed Aug. 15, 1955` Seymour ll. Richman, Cronlpond, and Leon M. Greenstein, New York, N. Y., assignors to Francis Earie Laboratories, Inc., Peekskill, N. Y., a corporation of New York Application August 15, 1955, Serial No. 528,367

8 Claims. 252-8) This invention relates to liquid hydrocarbon oil compositions useful for extinguishing magnesium res and res of magnesium alloys.

Magnesium and its alloys, and other alkaline earth metals such as calcium, `areextremely reactive. Since molten magnesium reactswith water, this most'common of extinguishing liquids cannot be used on magnesium tires. Indeed, the reaction between magnesium and Water produces hydrogen and the use of water adds theA dangers of explosion to those of the magnesium tire. Even exhaustion of available oxygen in the air is not suiiicient to extinguish magnesium fires, since nitrogen supports the combustion of the metal with the production of magnesium nitride. Carbon dioxide cannot be used as the extinguishing agent, since it too reacts with magnesium. Carbon tetrachloride similarly is not a suitable extinguishing agent because it reacts violently with the burning magnesium.

Because of the unsuitability of these common extinguishing materials, many of the agents which have been proposed have been solids. These generally depend on mixtures which exclude air mechanically. A mixture of potassium acid sulfate, trisodium phosphate, bauxite, and pumice is said to fuse around the magnesium mass at high temperatures, thereby excluding air. Another extinguishing agent consists of powdered graphite containing a small amount of high boiling liquid, tri (p-tert-butylphenyl) phosphate. The vaporization of the phosphate in the interstices between graphite particles forces out the air, while the graphite provides a cover over the hot metal mass. Solid extinguishing agents are best suited to small fires, where the powder can be applied to the burning surface manually, butrare not Well adapted to large res which cannot be closely approached. Since solid extinguishing agents for magnesium must be coated over the entire exposed surface, such agents are usually not suitable for use on large outdoor fires.

The uid extinguishers which have been proposed may be divided into two classes. In the first are those materials which protect the surface of the magnesium against further progress of the oxidation,l but which provide little or no cooling action. An example is boron trichloride liquid or vapor. A second class includes agents with high cooling capacity, but which offer little in the way of protection against further oxidation or ignition. High flash point petroleum or fatty oils fall in this class.

It is accordingly a basic objct of this invention to provide hydrocarbon oil compositionsV useful for extinguishing magnesium and magnesium alloy tires which oils have a high heat absorbing capacity and provide good protection against additional oxidation of the magnesium and prevent reignition of the metal.

lt is another object of the invention to provide extinguishing agents which are characteristically hydrocarbon liquids which are free-owing and can therefore be applied to tires from standard tire-fighting spray nozzles, pumps and simple mechanical equipment suitable for dispensing tire extinguishing fluids.

2,827,431 Patented Mar. 18, 1958 rc Y Other objects and advantages of the invention will in part be obvious and in part appear hereinafter.

The invention accordingly is embodied in a fire extinguishing agent in liquid form which is constituted of high ash point hydrocarbon oil having a high heat absorbing capacity blended with a second ingredient, so that the resultant composition is free-flowing, similar to water or a light lubricating oil, the combined mixture ofliquid substances therefore having at least one ingredient from each of two classes, the rst class being characterized as hydrocarbon oils of a high flash point with a high boiling point which they reach without substantial decomposition, the materials being further capable of absorbing large quantities of heat; the second ingredient being halogenated hyvdrocarbon gas such as methane or ethane or mixture of metal, thereby forming a protective coating and even a fusible coating at the burning surface. Y p

Within the class of hydrocarbon oils those having a high flash point atleast as high or higher than'that of kerosene, namely about 54 C., are vthe preferred materials because they will display boiling ranges starting from about 200 C. .The mineral oil should preferably beV completely volatile at the temperature of the burning metal.V VIf the oil contains a non-Volatile residue, decomposition will occur at the burning or hot surface. It lis important that the mineral oil constituent of this composition have this relatively high boiling point, because it is a characteristic part of the property of a high heat-absorbing capacity.

.In the extinguishing compositions used in this invention, the hydrocarbon liquids having the high heat absorbing capacity, constitute a rst group which includes oils having a `boiling range preferably above about 200 C. In addition to having high boiling points it is preferable that oils which do not decompose materially when heated to boiling be used. In general, oils which have been once distilled from the crude, that is, straightdistillate oils ranging in grade from fuel oils through lubricating oils are useful for the purpose. These are blended with the halogenated methane or ethane to give a free-flowing, nonviscous composition very useful for application to lires.

The property of decomposing prior to boiling causes the material to char and form an insulating layer at the burning metal surfaces so that the extinguishing characteristics of the composition, namely, its heat absorbing capacity and the effect of the halogenated hydrocarbon can not be brought into play. Such an insulating layer interferes with the cooling process but does not prevent the access of air, and therefore does not protect against further burnlng.

Therefore, fundamentally, the composition we employ is characterized by its using a hydrocarbon oil having a high boiling point and the further property of boiling without material decomposition, which material is employed for its high heat-absorbing capacity for the purpose of providing a rapid cooling of the burning magnesium. We blend it ,with a halogenated methane or ethane, such as methylbromide, methylenebromide, chlorobromomethane, ethylene dibromide or dichloride, diuorodibromomethane, etc. These materials are relatively volatile, have extremely low viscosities and when blended with the heavier oil give a resulting composition which is non-viscous and can be easily applied to the burning mass of metal. These compositions we have found remain free-ilowing even at temperatures as low as minus 50 to minus 60 F. and hence are useful in military installations in the Arctic regions or in airplanes at very high altitudes. These compositions can be sprayed on the burningmetal regardless of the ambient temperature in which they are stored and their cooling capacity is brought into play most rapidly as they gain access easily to all parts of the burning mass `of metal.

In the drawing, the apparatus used to evaluate the re extinguishing compositions is shown in diagrammatic form with the several parts identified.

In all fire extinguishing applications, it is desirable to remove heat as quickly vas possible, in order to reduce the flammable materials to temperatures below their ignition points. Water, as used in ordinary re extinguishing, is the most eicient heat absorber, because of its high heat capacity and its very high heat of Vaporization. No other common substance approaches its heat of vaporization of 540 calories per gram. Non-aqueous substances which are commonly used as vaporizing liquid extinguishers, such as carbon tetrachloride, derive their effectiveness from the exclusion of oxygen, and from breaking the chain of reactions involved in combustion, rather than from the absorption of heat; carbon tetrachloride, for example, has a heat of vaporization of only 46 calories per gram.

The re extinguishing compositions we use have a high heat absorbing capacity which renders them uniquely effective. The total heat absorbing capacity of the liquid not only depends on its heat of vaporization but on the heat capacity of the liquid as well, since it is the latter property which determines how much heat is absorbed in raising the liquid from ambient temperatures to the boiling point. may absorb more heat in attaining that temperature than is required to effect conversion from the liquid to the vapor state. With lower boiling compounds, however, it is likely that vaporization involves the absorption of more heat than the heating of the liquid to the boiling p temperature. I

The performance of magnesium lire extinguishing agents can be expressed in terms of the results of two re testing techniques. The rst test, designed to measure cooling eiciency, determines the quantity of agent necessary to reduce 15 pounds of burning magnesium to a temperature below its ignition point (approximately 650 C.). Since the burning metal generally attains a temperature of about 1050 C., a drop of 440 vC. is suicient to bring the temperature below 650 C. Thus M440 is dened as the weight of agent necessary to reduce the temperature of 15 pounds of burning magnesium by 440 C., and therefore represents the quantity required for complete extinguishing of the charge.

In the re test, carried out in the apparatus illustrated by the drawing, 15 pounds of magnesium or magnesium alloy are ignited in a cylindrical cavity 11.5

inches in diameter and 6 inches deep, in slightly moistened sand. A Chromel-Alumel thermocouple, which has been buried in the earth, emerges at the center of the cavity, so that the bimetallic junction is 1.5 inches above the floor of the cavity. The magnesium is ignited by means of an oxyacetylene torch. As the metal melts and burns, it lls the cavity uniformly. Forced air may be used to bring the metal to a temperature in the neighborhood of 1050 C. more rapidly. When this point is reached, the extinguishing agent is applied in a slow stream or spray at the rate of about one pound per minute. The agent is distributed over the surface of the burning mass by manipulation of the delivery pipe. Because of the rapid heat transfer from the burning magnesiurn to the agent, the distribution is not critical. The temperature is measured while the agent is applied; from the known rate of application, M440 may be calculated.

To test for protection against reignition, an essentially similar procedureis followed, with the exceptionV that the application of the extinguishing agent is discontinued when the temperature has fallen to 900 C., which is still 250 above the ignition temperature of magnesium. Furthermore, the sand cavity is linedV with a Icylindrical steel shell (24 gauge) open at both ends; the additional rigidity is necessary to maintain an approximately con- A liquid with a very high boiling point stant metal-air interface from test to test. The temperature measurements are continued after application has ceased. If there is adequate protection against reignition, the metal gradually cools. In the absence of such protection, the mass reignites, and the temperature increases. To put the results on a semi-quantitative basis, it is con- Venient'to cite the change in temperature twenty minutes after the application is discontinued; this ligure is presented as ATZO. The more negative the value `of ATZ, the more eiective is protection against reignition.

lIn Table I are given M440 and ATN values for a number of extinguishing agents.

TABLEl I Eciency of extinguishing agents on magnesium fires -Composition M440 ATM) Min. Oil1 CB2 y 1 Viscosity 335 to 350 Saybolt seconds at 100 F.

2CB-chlorobroxnomethane; DFDBdifluorodibrornomethane. These are representative halogenated hydrocarbons which give results typical of the halogenated methanes, ethanes, ete., which have been donned.

The secondary re in each case was much milder when the halogenated hydrocarbon was used. In re tests Where the primary purpose was rapid extinguishing rather than obtaining quantitative data, the presence of the halogenated hydrocarbon caused the secondary iire to be self-extinguished as excess extinguishing agent was rapidly added. This does not occur in the absence of the halogenated hydrocarbon.

In the above tabulation, it will be evident that mineral oil alone which was a paraln oil having a Saybolt viscosity of 335-350 seconds, at 100 F., was not a suitable kextinguishing agent as demonstrated by the ,positive AT value. Correspondingly, the second component of the composition, designated CB, which is chlorobromomethane, was likewise ineffective as an extinguishing agent as shown by the positive AT value. The mixtures wherein the two ingredients were present in weight ratio ranging from about one part of halogenated hydrocarbons to nine parts of mineral oil or from one part of mineral oil to about nine parts of halogenated hydrocarbon gave elective extinguishing properties. The compositions thus represent a blend which is a mild compromise with its heat absorbing capacity, but gives good protection against reignition and the reduction of the intensity of the secondary re. Although the proportion of materials from the hydrocarbon oil class and those from the halogenated hydrocarbon class may be varied it is best to stay in the range from 1 part to 3 parts by weight to 3 parts to 1 part by weight. Because the agents or" this invention are lluid and involve the use of one ingredient which has an extremely low viscosity, it is possible to use mineral oils of quite high boiling points and boiling ranges and quite high viscosities. Generally, there is no diiculty in obtaining the right degree of solubility of the one in the other because mineral oils are miscible in all proportions with the halogenated hydrocarbons described.

It is possible to modify the ultimate viscosity or ultimate physical properties of the extinguishing agents by using a combination of mineral oils or a combination of halogenated hydrocarbons. The combinations of the halogenated hydrocarbons arc generally directed toward the development of greater protection against reignition; that is, it appears that the bromide compounds are generally the most effective ones against the reignition of asomar the metal. A very great advantage in the blends of one compound from each class or in combinations of compounds from each class resides in the development of compositions which are permanently liquids of low viscosity and hence useful where storage in cold climates is required.

Magnesium and magnesium alloys, for example, those of aluminum, and other alkaline earth metals such as calcium all burn quite violently once they are started. Such tires can be extinguished using the agents described with results paralleling those shown for magnesium. That is, in each case the metal is cooled to a temperature below its ignition point, the tire is converted into a secondary one, and that is readily extinguished.

Though the invention has been described in terms of only a few examples it is apparent that variations thereof may be made without departing from its spirit or scope.

What is claimed is:

1. A liquid composition useful for extinguishing fires involving burning metal comprising a blend of a rst ingredient which is a hydrocarbon oil characterized by its high heat absorbing capacity and boiling range starting from about 200 C., said oil being further characterized by its substantially complete volatility at the temperature of the burning metal, and a second ingredient which is monochloromonobromomethane, said second ingredient reacting with the metal to form a protective coating to impede further oxidation, the proportions by weight of said ingredients being respectively from about three parts of the first to one part of the second to one part of the rst to three parts of the second.

6 2. A composition in accordance with claim 1, in which said iirst ingredient is a hydrocarbon oil having a Saybolt viscosity of about 350 seconds.

3. A composition in accordance with claim l, in which said irst ingredient is a kerosene.

4. A composition in accordance with claim l, in which said rst ingredient is a paraffin oil.

5. A liquid composition useful for extinguishing res involving burning metal comprising a blend of a first ingredient which is a hydrocarbon oil characterized by its high heat absorbing capacity and boiling range starting from about 200 C., said oil being further characterized by its substantially complete volatility at the temperature of the burning metal, and a second ingredient which is monochloromonobromomethane, said second ingredient reacting with the metal to form a protective coating to impede further oxidation, the proportions by weight of said ingredients being about equal.

6. A composition in accordance with claim 5, in which said rst ingredient is a hydrocarbon oil having a Saybolt viscosity of about 350 seconds.

7. A composition in accordance with claim 5, in which said first ingredient is a kerosene.

8. A composition in accordance with claim 5, in which said first ingredient is a parain oil.

References Cited n the le of this patent UNITED STATES PATENTS 

1. A LIQUID COMPOSITION USEFUL FOR EXTINGUISHING FIRES INVOLVING BURNING METAL COMPRISING A BLEND OF A FIRST INGREDIENT WHICH IS A HYDROCARBON OIL CHARACTERIZED BY ITS HIGH HEAT ABSORBING CAPACITY AND BOILING RANGE STARTING FROM ABOUT 200*C., SAID OIL BEING FURTHER CHARACTERIZED BY ITS SUBSTANTIALLY COMPLETE VOLATILITY AT THE TEMPERATURE OF THE BURNING METAL, AND A SECOND INGREDIENT WHICH IS MONOCHLOROMONOBROMOMETHANE, SAID SECOND INGREDIENT REACTING WITH THE METAL TO FORM A PROTECTIVE COATING TO IMPEDE FURTHER OXIDATION, THE PROPORTIONS BY WEIGHT OF SAID INGREDIENTS BEING RESPECTIVELY FROM ABOUT THREE PARTS OF THE FIRST TO ONE PART OF THE SECOND TO ONE PART OF THE FIRST TO THREE PARTS OF THE SECOND. 